Offsetting non-uniform brightness in a backlit display assembly via a spatial distribution of light extraction features

ABSTRACT

A headset includes a display block and an optics block. The display block includes a waveguide configured to receive light from a light source assembly, a plurality of extraction features that have a spatial distribution across one or more surfaces of the waveguide, wherein the plurality of extraction features out-couple light from the waveguide, and the spatial distribution is such that out-coupled light has a first non-uniform brightness distribution, and a display panel configured to modulate the out-coupled light to form image light, wherein the image light has a brightness distribution based in part on the first non-uniform brightness distribution. The optics block includes optical elements configured to direct the image light to an eyebox, and the optics block adds a second non-uniform brightness distribution that is offset by the first non-uniform brightness distribution, such that the image light directed to the eyebox has a target brightness distribution.

BACKGROUND

This disclosure relates generally to backlit displays, and specificallyto using offsetting non-uniform brightness in a backlit display assemblyvia a spatial distribution of light extraction features.

Some conventional head-mounted displays (HMDs) include components in theoptical path of a display of the HMD that can result in non-uniformbrightness of a displayed image. For example, in a backlit display, adisplay panel may cause a non-uniform brightness in the image light. Thenon-uniform brightness degrades image quality and can adversely affect auser's use of the HMD.

SUMMARY

A spatial distribution of light extraction features is used to offsetnon-uniform brightness. The display block includes a waveguide, aplurality of extraction features, and a display panel. The waveguide isconfigured to receive light from a light source assembly. The pluralityof extraction features have a spatial distribution across one or moresurfaces (e.g., front surface and/or back surface) of the waveguide. Theplurality of extraction features out-couple light from the waveguide(e.g., in a direction of an eyebox), and the spatial distribution issuch that out-coupled light has a first non-uniform brightnessdistribution. The display panel is configured to modulate theout-coupled light to form image light. The image light has a brightnessdistribution based in part on the first non-uniform brightnessdistribution.

The image light may then be passed through an optics block. The opticsblock includes a first optical element and a second optical element thattogether generate a folded optical system that is configured to directthe image light to an eyebox. The folded optical system adds a secondnon-uniform brightness distribution that is offset by the firstnon-uniform brightness distribution, such that the image light directedto the eyebox has a target brightness distribution. In some embodiments,the display block and the optics block may be part of a headset.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a headset, in accordance with one or moreembodiments.

FIG. 2 is a cross-section of a front rigid body of the headset in FIG.1, in accordance with one or more embodiments.

FIG. 3 is a diagram showing a backlit display assembly, in accordancewith one or more embodiments.

FIG. 4 is a cross-section of a waveguide with extraction features, inaccordance with one or more embodiments.

FIG. 5 is a cross-section of an extraction feature on a waveguide, inaccordance with one or more embodiments.

FIG. 6 is a diagram of a display block with a plurality of extractionfeatures arranged in a spatial distribution on a front surface of awaveguide, in accordance with one or more embodiments.

FIG. 7 is a block diagram of an artificial reality system, in accordancewith one or more embodiments.

The figures depict various embodiments for purposes of illustrationonly. One skilled in the art will readily recognize from the followingdiscussion that alternative embodiments of the structures and methodsillustrated herein may be employed without departing from the principlesdescribed herein.

DETAILED DESCRIPTION

Overview

A headset for displaying images includes a display block with a lightsource assembly that provides light to a waveguide with extractionfeatures distributed across one or more surfaces of the waveguide. Theextraction features out-couple light from the waveguide in a directiontowards a display panel, with the out-coupled light having a firstnon-uniform brightness distribution dependent on a spatial distributionof the extraction features. The display panel modulates the out-coupledlight to form image light which has a brightness distribution. An opticsblock, including one or more elements, directs the image light to theeyebox.

At least one component of the headset introduces a non-uniformbrightness distribution that is offset by the first non-uniformbrightness distribution generated by the spatial distribution of theextraction features. For example, the display panel and/or the opticsblock may introduce a non-uniform brightness distribution that is offsetby the first non-uniform brightness distribution to provide a targetbrightness distribution of image light at the eyebox. In someembodiments, the optics block includes optical elements that form afolded optical system, such as a pancake lens assembly. The spatialdistribution of the extraction features on the waveguide offsets errorsin the brightness distribution of the image light at the eyeboxintroduced by the folded optical system. The spatial distribution of theextraction features may be non-uniform. For example, a density of anumber of extraction features per unit area may be relatively low nearan optical axis of the display block and relatively high at distancesfarther from the optical axis. In this manner, the spatial distributionof extraction features can be tailored to offset any undesirablenon-uniformity in the brightness distribution of a displayed imagecaused by one or more components of the headset.

Embodiments of the present disclosure may include or be implemented inconjunction with an artificial reality system. Artificial reality is aform of reality that has been adjusted in some manner beforepresentation to a user, which may include, e.g., a virtual reality (VR),an augmented reality (AR), a mixed reality (MR), a hybrid reality, orsome combination and/or derivatives thereof. Artificial reality contentmay include completely generated content or generated content combinedwith captured (e.g., real-world) content. The artificial reality contentmay include video, audio, haptic feedback, or some combination thereof,and any of which may be presented in a single channel or in multiplechannels (such as stereo video that produces a three-dimensional effectto the viewer). Additionally, in some embodiments, artificial realitymay also be associated with applications, products, accessories,services, or some combination thereof, that are used to, e.g., createcontent in an artificial reality and/or are otherwise used in (e.g.,perform activities in) an artificial reality. The artificial realitysystem that provides the artificial reality content may be implementedon various platforms, including a headset or head-mounted display (HMD)connected to a host computer system, a standalone NED, a mobile deviceor computing system, any other hardware platform capable of providingartificial reality content to one or more viewer, or some combinationthereof.

Headset

FIG. 1 is a diagram of a headset 100, in accordance with one or moreembodiments. In the illustrated embodiments, the headset 100 is a HMD.The headset 100 may be part of an artificial reality system. Inembodiments that describe AR system and/or a MR system, portions of afront side 110 of the headset 100 are at least partially transparent inthe visible band (˜380 nm to 750 nm), and portions of the headset 100that are between the front side 110 of the headset 100 and an eye of theuser are at least partially transparent (e.g., a partially transparentelectronic display).

The headset 100 provides content (e.g., virtual, augmented, etc.) to awearer. The headset 100 includes a front rigid body 120 and a band 130.The front rigid body 120 includes a depth camera assembly (not shown),an illumination aperture 140, an imaging aperture 150, a backlit displayassembly (not shown), an Inertial Measurement Unit (IMU) 170, one ormore position sensors 180, and the reference point 190.

The depth camera assembly (DCA) is configured to determine depthinformation of a local area surrounding some or all of the headset 100.An illumination source of the DCA emits infrared light (e.g., structuredlight, flash illumination for time-of-flight, etc.) through theillumination aperture 140. An imaging device of the DCA captures lightfrom the illumination source that is reflected from the local areathrough the imaging aperture 150. The DCA determines depth informationfrom the local area using the captured images.

The backlit display assembly is configured to present content. Asdescribed below with regard to FIGS. 2-6, the backlit display assemblyincludes an optics block and a display block. The display blockgenerates image light that includes a non-uniform brightnessdistribution that is used to offset errors in brightness caused by,e.g., components of the optics block and/or a display panel of thedisplay block. The non-uniform brightness distribution of the imagelight may be an error brightness distribution which results inunintended errors in the image viewed by the user. The optics blockdirects the image light to an eyebox for each eye of a wearer.

The IMU 170 is an electronic device that generates IMU data based onmeasurement signals received from one or more of the position sensors180. The reference point is a point that may be used to describe theposition of the headset 100. A position sensor 180 generates one or moremeasurement signals in response to motion of the headset 100. Examplesof position sensors 180 include: one or more accelerometers, one or moregyroscopes, one or more magnetometers, another suitable type of sensorthat detects motion, a type of sensor used for error correction of theIMU 170, or some combination thereof. In the embodiment shown by FIG. 1,the position sensors 180 are located within the IMU 170, and neither theIMU 170 nor the position sensors 180 are visible to a user of theheadset 100. The position sensors 180 may be located external to the IMU230, internal to the IMU 230, or some combination thereof.

FIG. 2 is a cross-section 200 of the front rigid body 120 of the headset100 in FIG. 1, in accordance with one or more embodiments. As shown inFIG. 2, the front rigid body 120 includes backlit display assembly 205and a DCA 210.

The backlit display assembly 205 provides image light to an eye-box 215.The eye-box 215 is the location of the front rigid body 120 where auser's eye 220 is positioned. For purposes of illustration, FIG. 2 showsa cross section 200 associated with a single eye 220, but anotherbacklit display assembly 205, separate from the backlit display assembly205, may provide image light to another eye of the user. In someembodiments, a single backlit display assembly 205 may provide imagelight to both of a user's eyes. The backlit display assembly 205includes a display block 225 and an optics block 230.

The display block 225 generates image light that includes a non-uniformbrightness distribution. The non-uniform brightness distribution offsetserrors in brightness caused by the display block 225, the optics block230, some other component of the headset 100, or some combinationthereof. The display block is discussed in detail below with regard toFIG. 3.

The optics block 230 directs light received from the display block tothe eye box 215. The optics block 230 includes one or more opticalelements that direct the image light to the eye box 215. An opticalelement may be an aperture, a Fresnel lens, a refractive lens, areflective surface, a waveplate (e.g., quarter wave plate), adiffractive element, a waveguide, a reflector (full reflector or apartial reflector), a filter, any other suitable optical element thataffects the image light emitted from the display block 225, or somecombination thereof. Moreover, the optics block 230 may includecombinations of different optical elements. In some embodiments, one ormore of the optical elements in the optics block 230 may have one ormore coatings, such as anti-reflective coatings, dichroic coatings, etc.In some embodiments, there are a plurality of optical elements,including at least a first optical element and a second optical element,that together form a folded optical system (i.e., the light is reflectedback towards the display block 225 at least once before exiting theoptics block 230). In some embodiments, a pancake lens assembly is anexample, of a folded optical system. Additional details of a pancakelens assembly may be found at, e.g., U.S. patent application Ser. No.15/441,738, U.S. patent application Ser. Nos. 15/335,807, and 15/179,883which are hereby incorporated by reference in their entirety.

The optics block 230 may add a non-uniform brightness distribution thatis offset by the non-uniform brightness distribution of the image lightemitted by the display block 225, such that the image light directed tothe eye box 215 has a target brightness distribution. The targetbrightness distribution is a brightness distribution of the image lightwhere non-uniformities introduced by the optics block 230, the displayblock 225, some other component of the headset 100, or some combinationthereof, have been reduced to less than some threshold value (e.g. lessthan 1%).

In some embodiments, the optics block 230 magnifies received light fromthe display block 225 and corrects optical aberrations associated withthe image light, and the corrected image light is presented to a user ofthe headset 100. Magnification of the image light by the optics block230 allows elements of the display block 225 to be physically smaller,weigh less, and consume less power than larger displays. Additionally,magnification may increase a field-of-view of the displayed media. Forexample, the field-of-view of the displayed media is such that thedisplayed media is presented using almost all (e.g., 110 degreesdiagonal), and in some cases all, of the user's field-of-view.

As shown in FIG. 2, the front rigid body 120 further includes the DCA210 for determining depth information of one or more objects in a localarea 235 surrounding some or all of the headset 100. The DCA 210includes a light generator 240, an imaging device 245, and a controller250 that may be coupled to both the light generator 240 and the imagingdevice 245. The light generator 240 emits light through the illuminationaperture 140. In accordance with embodiments of the present disclosure,the light generator 240 is configured to illuminate the local area 235with structured light 255 in accordance with emission instructionsgenerated by the controller 250. The controller 250 is configured tocontrol operation of certain components of the light generator 240,based on the emission instructions. The controller 285 provides theemission instructions to a plurality of diffractive optical elements ofthe light generator 240 to control a field-of-view of the local area 235illuminated by the structured light 255.

The light generator 240 may include a plurality of emitters that eachemits light having certain characteristics (e.g., wavelength,polarization, coherence, temporal behavior, etc.). The characteristicsmay be the same or different between emitters, and the emitters can beoperated simultaneously or individually. In one embodiment, theplurality of emitters could be, e.g., laser diodes (e.g., edgeemitters), inorganic or organic LEDs, a vertical-cavity surface-emittinglaser (VCSEL), some other source, or some combination thereof. In someembodiments, a single emitter or a plurality of emitters in the lightgenerator 240 can emit light having a structured light pattern.

The imaging device 245 includes one or more cameras configured tocapture, through the imaging aperture 150, portions of the structuredlight 255 reflected from the local area 235. The imaging device 245captures one or more images of one or more objects in the local area 235illuminated with the structured light 255. The controller 250 is alsoconfigured to determine depth information for the one or more objectsbased on the captured portions of the reflected structured light. Insome embodiments, the controller 250 provides the determined depthinformation to a console (not shown in FIG. 2). The console and/or theheadset 100 may utilize the depth information to, e.g., generate contentfor presentation by the backlit display assembly 205.

FIG. 3 is a diagram showing the backlit display assembly 205, inaccordance with one or more embodiments. The backlit display assembly205 includes embodiments of the display block 225 and the optics block230. In other embodiments, the backlit display assembly 205 may includeadditional components than those illustrated.

The display block 225 generates image light having a first non-uniformbrightness distribution. The display block 225 includes a light sourceassembly 305, a waveguide 310, and a display panel 315. In someembodiments, the display block 225 may include additional components.For example, the display block 225 may include a diffuser between thewaveguide 310 and the display panel 315.

The light source assembly 305 generates light in a first optical band.The light source assembly 305 includes one or more source elements thatgenerate light in the first optical band. The first optical bandincludes at least light in the visible band. A source element may be,for example, a light emitting diode (LED), an organic LED (OLED), alaser diode, a vertical-cavity surface-emitting lasers (VCSEL), amicro-LED, some other device that emits light in the first optical band,or some combination thereof. The light source assembly 305 may include aplurality of source elements that emit light in one or more colorchannels of the visible band (e.g., red, green, blue, white, etc.). Insome embodiments, the light from the light source assembly 305 iscoupled into the waveguide 310 in a direction different from an opticalaxis 320 of the backlit display assembly 205. In other embodiments thelight source assembly 310 may be positioned different from what is shownin FIG. 3

The waveguide 310 directs the light from the light source assembly 305towards the display panel 315. The waveguide 310 includes an incouplingarea 325 a front surface 330, and a back surface 335 that is opposite tothe front surface 330. The optical axis 320 intersects the front surface330 at a center point 340. Light is incoupled into the waveguide 310 atthe incoupling area 325. In some embodiments, the waveguide 310 isformed from an optically transparent material. For example, thewaveguide 310 may be formed of glass, plastic, semiconductor material,any other material that is substantially transparent to light in thefirst optical band, or some combination thereof. In some embodiments,the waveguide 310 has a curvature and is not flat. In some embodiments,the incoupled light propagates through the waveguide 310 via totalinternal reflection (TIR). In some embodiments, one or both of the frontsurface 330 and the back surface 335 may be coated with at least apartially reflecting surface. For example, the back surface may becoated with a 100% reflective surface (for light in the visible band)and the front surface 330 may be coated with an 80% reflective surface(for light in the visible band).

One or both of the front surface 330 and/or the back surface 335 mayinclude extraction features that cause light to outcouple from thewaveguide 310 (e.g., towards the display panel 315). For example, in theillustrated embodiment, the front surface 330 includes a plurality ofextraction features that includes the extraction feature 345.

The extraction features are arranged along one or both of the frontsurface 330 and/or the back surface 335 in a spatial distribution whichintroduces the first non-uniform brightness distribution in theout-coupled light. The first non-uniform brightness distribution offsetserrors in brightness distribution caused by other components of theheadset (e.g., the display panel 315 and/or the optics block 230). Ahigher spatial density of extraction features in a region of thewaveguide 310 (relative to other regions of the waveguide 310 with alower spatial density of extraction features) results in an increase inout-coupled light at the region (relative to the other regions). Thespatial distribution of extraction features is determined based onerrors in the brightness distribution that are introduced by othercomponents of a headset. For example, if the other components are knownto cause dimness in a peripheral region of the displayed image (relativeto other portions of the displayed image), the spatial distribution ofextraction features is designed such that a density of extractionfeatures along the periphery of the waveguide 310 that generallycorresponds to the peripheral region of the displayed image is higherthan other areas (e.g., a central region) of the waveguide 310. Such aspatial distribution of extraction features thereby can create anon-uniform brightness distribution that offsets the dimness along theperipheral region of the displayed image, resulting in the displayedimage having a target brightness distribution. Accordingly, by adjustingthe spatial distribution of extraction features such that it is higherin some areas and lower in other areas, a non-uniform brightness profileis created in the out-coupled light that mitigates errors in brightnessdistribution caused by other components of the headset.

The display panel 315 modulates the out-coupled light from the waveguide310 to form image light corresponding to image content to be displayedto the user. The display panel 315 spatially modulates the out-coupledlight in the first optical band received from the waveguide 310. In someembodiments, the display panel 315 includes a color filter arrayoverlaying a liquid crystal array. The color filter array may be, e.g.,a Bayer pattern, another color pattern, or some combination thereof.Out-coupled light in the first optical band from the waveguide 310 ismodulated by the color filter array and the liquid crystal array to formthe image light. In some embodiments, the display panel may includeadditional optical elements. In some embodiments, the display panel 315has a curvature and is not flat. For example, the display panel 315 mayhave a curvature that matches a curvature of the waveguide 310. Thedisplay panel 315 transmits the image light towards the optics block230.

The display panel 315 may introduce a non-uniform brightnessdistribution to the image light displayed to the user that is offset bythe first non-uniform brightness distribution of the spatialdistribution of extraction features. For example, the image lighttransmitted from the periphery of the display panel may be less brightthan at the center of the display panel 315. In some cases, thebrightness of the transmitted image light may decrease as a function ofdistance from the optical axis 320 or the center point 340. Thenon-uniform brightness introduced by the display panel 315 is notlimited to exemplary spatial relationships discussed above, and someembodiments may include other non-uniform brightness distributions withdifferent spatial relationships.

The optics block 230 directs light transmitted from the display panel315 to the eye box 215 along the optical axis 320. In the illustratedembodiment, the optics block 230 includes a first optical element 350and a second optical element 355, that together form a folded opticalsystem. In the illustrated embodiments, the folded optical system is apancake lens assembly. Note that one or both of the optical element 350and the optical element 355 may impart optical power to the light (e.g.,have curved front and/or back surfaces). For example, in one embodimentof a pancake lens assembly, the optical element 350 includes a backsurface 360 coated with a partial reflector (e.g., 50:50 reflector), anda front surface 365 coated with a quarter waveplate. And the opticalelement 355 includes a back surface 370 coated with a quarter waveplateand a front surface 375 coated with a reflective linear polarizer. Insome embodiments, the back surface 360 may also have a linear polarizercoated on top of the partial reflector.

In some embodiments, the optics block 230 includes more than two opticalelements forming a folded optical system. For example, the optics block230 may include four optical elements forming a folded optical system.Additional details of a pancake lens assembly may be found at, e.g.,U.S. patent application Ser. No. 15/441,738, U.S. patent applicationSer. Nos. 15/335,807, and 15/179,883 which are hereby incorporated byreference in their entirety. Embodiments of the optics block 230 are notlimited to the examples discussed herein.

The optics block 230 may add a non-uniform brightness that is offset bythe non-uniform brightness distribution of the image light emitted bythe display block 225. The non-uniform brightness distribution added bythe optics block 230 is also referred to herein as an errordistribution. For example, the error distribution may have a lowerbrightness of image light at a peripheral region that circumscribes acenter region than in the center region. In some cases, the errordistribution may have a brightness of the image light decreasing as afunction of distance from the optical axis 320 or the center point 340.The error distribution introduced by the optics block 230 is not limitedto exemplary spatial relationships discussed above, and some embodimentsmay include other non-uniform brightness distributions with differentspatial relationships.

The image light that is delivered to the eyebox 215 has a targetbrightness distribution as a result of the error distribution of theoptics block 230 being offset by the non-uniform brightness distributionof the display panel 315, which is in turn offset by the firstnon-uniform brightness distribution of the spatial distribution ofextraction features. The spatial distribution of extraction featuresprovides the benefit of offsetting any unintended errors in thebrightness distribution that may otherwise exist in the image lightdelivered to the eyebox 215, resulting in the target distribution.Different configurations of the spatial distribution may be used toachieve various target brightness distributions. The target brightnessdistribution is a brightness distribution of the image light wherenon-uniformities introduced by the optics block 230, the display block225, some other component of the headset 100, or some combinationthereof, have been reduced to less than some threshold value (e.g. lessthan 1%).

In some embodiments, the non-uniform brightness distribution of thedisplay panel 315 and the error distribution of the optics block 230together result in image light at the eyebox 215 with a lower brightnessin a peripheral region than in a center region that is circumscribed bythe peripheral region, the extraction features of the waveguide have acorresponding spatial distribution. In this case, the peripheral regionis further away from the optical axis 320 than the center region. Tooffset errors in brightness in the image light, the spatial distributionof extraction features includes a higher spatial density of extractionfeatures in the peripheral region than in the center region. Theincrease in light out-coupled from the waveguide 310 at the peripheralregion off-sets the decrease in image light at the peripheral regionsdue to the display block and the optics block 230, resulting in a targetbrightness distribution that is spatially uniform within a tolerance(e.g. less than 1% spatial variation in brightness).

While the exemplary embodiments discussed above feature a peripheralregion and a center region, embodiments of the present disclosure arenot limited to such configuration. Other embodiments may includedifferent regions with different corresponding spatial densities ofextraction features than what is discussed in the above example.

In some embodiments, the backlit display assembly 205, including thedisplay block 225 and optics block 230, are configured to deliver lightto a user in order to display image content to a user of the headset100. The light source assembly 305 incouples light into the waveguide310 through an incoupling area 325. The light travels through thewaveguide 310 in a direction different from the optical axis 320. Theextraction features 345 out-couple the light in a direction towards thedisplay panel 315 along the optical axis 320. The display panel 315spatially modulates the out-coupled light to form image light which ismanipulated and directed towards the eyebox of a user by the opticsblock 230. The spatial distribution of the extraction features 345offsets errors in the brightness distribution of image light directedtowards the eyebox, which may be introduced by the display panel 315and/or the optics block 230 (and/or potentially other components). Thus,reducing changes of poor user experiences with the headset 100 due toerrors (e.g., un-intended non-uniformities) in the brightnessdistribution of image light.

Light Extraction

FIG. 4 is a cross-section 400 of a waveguide 410 with extractionfeatures 420, in accordance with one or more embodiments. The waveguide410 is an embodiment of the waveguide 310. Light from the light sourceassembly 305 is incoupled into the waveguide 410, and the light travelsinternally in the waveguide along a direction that is different than theoptical axis 320.

The waveguide 410 includes a plurality extraction features 420 thatout-couple light from the waveguide 420 to form out-coupled light 430.For ease of illustration a portion of the plurality of extractionfeatures 420 are illustrated in FIG. 4. Moreover, while the extractionfeatures 420 illustrated in FIG. 4 occur along an axis that issubstantially parallel to the y-axis for a fixed value of x, theplurality of extraction features on the waveguide 410 are more generallydistributed across a plane that is substantially parallel to a planeformed by the x and y axis. The out-coupled light may be directed towarda display panel (e.g., the display panel 315) and/or some intermediateoptical element prior to the display panel.

A spatial distribution of the extraction features 420 on a surface ofthe waveguide 410 introduces a first non-uniform brightness distributionto the out-coupled light 430 that is used to offset errors in brightnesscaused by components of a headset (e.g., components of the optics block230, a display panel 315, another component, or some combinationthereof). For example, a display panel may introduce errors in thebrightness distribution of the image light provided to an optics block(e.g., the optics block 230). Likewise, the optics block may introduceerrors in the brightness distribution of the image light directedtowards an eyebox. These errors in the brightness distribution maygenerally be described as non-uniformities in the brightnessdistribution. The spatial distribution of the extraction features 420 issuch that the first non-uniform brightness distribution of theout-coupled light 430 offsets the errors introduced into the brightnessdistribution of the image light by other components of the headset,thereby, resulting in a target brightness distribution of the imagelight at the eyebox. The target brightness distribution is a brightnessdistribution for providing image content to a user. In some embodiments,the target brightness distribution is a uniform brightness distribution.

As shown in FIG. 4, the spatial distribution of extraction features 460includes a center region 440 and a peripheral region 450 thatcircumscribes the center region 450. A spatial density (extractionfeature per unit area) of the extraction features 420 is higher in theperipheral region 450 than in the center region 440. The higher densityof extraction features 420 in the peripheral region 450 results in anincreased amount of out-coupled light in the peripheral region 450.Thus, the first non-uniform brightness distribution in the out-coupledlight 430 is be spatially modulated such that the out-coupled light 430in the peripheral region 450 is brighter than the out-coupled light 430in the center region 440. In this case, the first non-uniform brightnessdistribution of the out-coupled light 430 offsets an error in brightnessdistribution (e.g., a dimming of light relative to other portions of theimage light) at the peripheral region 450 introduced by other componentsof the headset 100, resulting in a target brightness distribution at theeyebox 215 that has significantly reduced spatial non-uniformities.Other embodiments may include other types of errors in brightnessdistribution introduced by components of the headset 100 other than adimming at the peripheral region 450. In such cases, other spatialdistributions of the extraction features 420 may correspond to theerrors in brightness distribution.

In alternate embodiments, the extraction features 420 may have a lowerspatial density in the peripheral region 450 than in the center region440, and thus may have a lower brightness of out-coupled light 430 inthe peripheral region 450 than in the center region 440. In someembodiments, the spatial density of the extraction features 420 in theperipheral region 450 increases as a function of distance from a centerpoint 460. The center point 340 is an on-axis intersection point of thewaveguide 410 and the optical axis 320. In some embodiments, a spatialdistribution of the extraction features 420 are symmetric with respectto an axis parallel to the x-axis and/or an axis parallel to the y-axis,are rotationally symmetric about the optical axis 320, are rotationallysymmetric about some axis parallel to the optical axis 320, or somecombination thereof. In some embodiments, the spatial distribution ofextraction features 420 is asymmetric with respect to an axis parallelto the x-axis and/or an axis parallel to the y-axis.

Additionally, embodiments of the present disclosure are not limited toconfigurations with a center region and a peripheral region, asillustrated in FIG. 4. In some embodiments, the spatial density of theextraction features 420 is not dependent on a region and increases as afunction of distance from the center point 760. Although the spatialdistribution is shown in FIG. 4 includes the center region 440 and theperipheral region 450, the spatial distribution may have more regionswith various configurations of shape, size, and spatial density ofextraction features 420 in each region. In other embodiments, thespatial distribution is configured with other variations of the spatialdensity of the extraction features 460.

The waveguide 410 may provide out-coupled light 430 towards a displaypanel and optics block. The spatial distribution of the extractionfeatures 420 may provide a first non-uniform brightness distribution inthe out-coupled light 430 that offsets errors in the brightness of lightdelivered to an eyebox introduced by the optics block, the displayblock, other components of the headset 100, or some combination thereof,resulting in a target brightness distribution. The target brightnessdistribution may correspond to an optimal viewing experience of imagecontent for a user, free of errors in the brightness of light deliveredto the eyebox.

FIG. 5 is a cross-section of an extraction feature on a waveguide 510,in accordance with one or more embodiments. The waveguide 510 is anembodiment of the waveguide 410 shown in FIG. 4. As shown in FIG. 5,light propagates in the waveguide 510 by internal reflection (e.g., TIR)along a direction that is different than the optical axis 320, and isout-coupled from the waveguide 510 by an extraction feature 520. Theextraction feature 520 is an embodiment of one of the extractionfeatures 420 shown in FIG. 4. The extraction feature 520 may have one ofseveral forms, for example a concave micro-dome structure, as shown inFIG. 5. Other embodiments include an extraction feature that are, e.g.,a pyramid structure, a convex micro-dome structure, a protruding dotstructure, a polyhedral structure, a prism structure, some otherstructure that cause light to out-couple from the waveguide, or somecombination thereof. The extraction feature 520 may have a size rangingfrom a few nanometers in width to a few millimeters in width. The sizeof the extraction feature 520 may correspond to a wavelength light inthe first optical band. The extraction feature 520 may be formed of thesame material as the waveguide 510 and may be optically transparent, butmay also be formed of a different material from the waveguide and mayhave an opacity different than the waveguide 510.

Light incident at the extraction feature 520 is not internallyreflected, due to an incidence angle lower than a critical angle of thewaveguide 520, and as a result out-couples through a surface of thewaveguide 510 that the extraction feature 520 is provided on. Likewise,in embodiments where an extraction feature is located on a back surface530 of the waveguide 510, the extraction feature bends the light suchthat its next incidence on a front surface 540 is less than the criticalangle, thereby, causing the light to out-couple from the waveguide 510.

Out-coupled light 430 from the waveguide 520 may then travels, e.g.,towards and through a display panel along the optical axis 320, asillustrated in FIG. 3. In some embodiments, the optical axis 320 isperpendicular to the direction of the light source assembly; however,embodiments of the present disclosure are not limited to thisarrangement. In some embodiments the waveguide 510 has a curvature andis not flat as shown in FIG. 5.

Spatial Distribution of Extraction Features

FIG. 6 is a diagram of a display block 600 with a plurality ofextraction features 610 arranged in a spatial distribution 620 on afront surface of a waveguide 630, in accordance with one or moreembodiments. The display block 600 is an embodiment of the display block225. Light from a light source assembly 605 is incoupled to thewaveguide 630 through an incoupling area (not shown) and travels throughthe waveguide 630 via total internal reflection. The light sourceassembly 605 is an embodiment of the light-source assembly 305. Theincoupled light from the light source assembly 605 is incident in adirection along the y-axis. The extraction features then out-couple thelight, directing it in a direction along an optical axis (not shown)which is coming out of the page parallel to the z-axis. The optical axisintersects the front surface of the waveguide 630 at a center point 640.

The spatial distribution 620 of extraction features introduces a firstnon-uniform brightness distribution to the out-coupled light which mayoffset errors in a brightness distribution caused by other components ofthe headset 100. As shown in FIG. 6, the spatial distribution 620features a higher spatial density of extraction features 610 as afunction of distance from the center point 640. In this case, thespatial density of extraction features 610 is higher at a periphery ofthe waveguide 630 than near the center point 640, resulting in a firstnon-uniform brightness distribution with a higher brightness ofout-coupled light at the periphery than at the center. The firstnon-uniform brightness distribution may offset a dimming of the imagelight at a periphery introduced by other components of a headset 100,thereby, resulting in a target brightness distribution. In someembodiments, the target brightness distribution is a spatially uniformdistribution within a tolerance. The tolerance, for example may be 1% orless spatial variations in brightness.

In some embodiments, the headset 100 includes two display blocks 600 forproviding image light to each eye of a user. In other embodiments, theheadset 100 may include a single display block for providing image lightto both eyes of a user. In some embodiments, the display block may notdeliver light to an eye of a user, but to some other object or surface.For example, display block may be part of a projection system thatprojects image light onto a wall. And the spatial distribution ofextraction features are used to offset errors in the brightness profilecaused by other components of the projection system.

As illustrated in FIG. 6, the spatial density of extraction features 610increases in both the y-dimension and the x-dimension, as a function ofdistance from the center point 640. In other embodiments, the spatialdistribution 620 may have other configurations. For example, the spatialdensity of extraction features 610 may vary in one of either thex-dimension or the y-dimension, but not the other. In some embodiments,the spatial distribution 620 may be symmetric in respect to an axisparallel to the x-axis, symmetric in respect to an axis in respect tothe y-axis, or rotationally symmetric in respect to the optical axis(not shown) parallel to the z-axis and intersecting the center point640. Other embodiments may include a spatial distribution 620 thatvaries with an angle from a reference direction, for example with anangle relative to the y-axis. In other embodiments, the light sourceassembly 605 may be positioned differently than shown in FIG. 6 with anincoupling area having a different orientation. For example, the lightsource assembly 605 may be positioned on a left side of the waveguide630, and the incoupling area may be a left face of the waveguide 630. Inthis case, incident light from the light source assembly 605 is directedin a direction along the x-axis.

In some embodiments, the waveguide 630 is curved. A front surface or aback surface of the waveguide 630 may not be flat with respect to thez-axis.

The display block 600 may provide image light to other components of theheadset 100 which manipulate and/or direct the image light. The spatialdistribution 620 of extraction features 610 provide a first non-uniformbrightness distribution which may offset errors in brightness introducedby the other components of the headset 100. The use of the spatialdistribution 620 of extraction features 610 allows a freedom of designfor the headset 100, where errors in the brightness distributionintroduced by the other components of the headset 100 do not limit ordegrade the image quality of the headset 100.

System Environment

FIG. 7 is a block diagram of an artificial reality system 700, inaccordance with one or more embodiments. The artificial reality system700 may operate in an artificial reality system environment. In someembodiments, the artificial reality system 700 shown by FIG. 7 comprisesa headset 705 and an input/output (I/O) interface 710 that is coupled tothe console 715. While FIG. 7 shows an example artificial reality system700 including one headset 705 and one I/O interface 710, in otherembodiments any number of these components may be included in theartificial reality system 700. For example, there may be multipleheadsets 705 each having an associated I/O interface 710, with eachheadset 705 and I/O interface 710 communicating with the console 715. Inalternative configurations, different and/or additional components maybe included in the artificial reality system 700. Additionally,functionality described in conjunction with one or more of thecomponents shown in FIG. 7 may be distributed among the components in adifferent manner than described in conjunction with FIG. 7 in someembodiments. For example, some or all of the functionality of theconsole 715 is provided by the headset 705.

The headset 705 presents content to a user comprising virtual and/oraugmented views of a physical, real-world environment withcomputer-generated elements (e.g., two-dimensional (2D) orthree-dimensional (3D) images, 2D or 3D video, sound, etc.). The headset705 may be, e.g., a HMD or a NED that includes a display block (e.g.,the display block 225). In some embodiments, the presented contentincludes audio that is presented via an external device (e.g., speakersand/or headphones) that receives audio information from the headset 705,the console 715, or both, and presents audio data based on the audioinformation. The headset 705 may comprise one or more rigid bodies,which may be rigidly or non-rigidly coupled together. A rigid couplingbetween rigid bodies causes the coupled rigid bodies to act as a singlerigid entity. In contrast, a non-rigid coupling between rigid bodiesallows the rigid bodies to move relative to each other. An embodiment ofthe headset 705 is the headset 100 described above in conjunction withFIG. 1.

The headset 705 includes a DCA 720, a display block 725, an optics block730, one or more position sensors 735, and an IMU 740. Some embodimentsof the headset 705 have different components than those described inconjunction with FIG. 7. Additionally, the functionality provided byvarious components described in conjunction with FIG. 7 may bedifferently distributed among the components of the headset 705 in otherembodiments.

The DCA 720 captures data describing depth information of an areasurrounding some or all of the headset 705. The DCA 720 can compute thedepth information using the data (e.g., based on captured portions ofstructured light), or the DCA 720 can send this information to anotherdevice such as the console 715 that can determine the depth informationusing the data from the DCA 720.

The DCA 720 includes a light generator, an imaging device, and acontroller that may be coupled to both the light generator and theimaging device. The light generator of the DCA 720 is configured toilluminate a local area with structured light in accordance withemission instructions from the controller. The structure light may be inan infrared band. The imaging device of the DCA 720 is configured tocapture one or more images of portions of the structured light reflectedfrom one or more objects in the local area. The controller of the DCA720 generates the emission instructions and provides the emissioninstructions to the light generator of the DCA 720. The controller ofthe DCA 720 is also configured to determine depth information for theone or more objects based at least in part on the captured one or moreimages of portions of the reflected structured light.

The display block 725 displays 2D or 3D images to the user in accordancewith data received from the console 715. In various embodiments, thedisplay block 725 comprises a single electronic display or multipleelectronic displays (e.g., a display for each eye of a user). In someembodiments, the display block includes a light source assembly, awaveguide, and a display panel. The light source assembly provides lightthat is coupled into the waveguide which directs the light towards aneyebox of the user through the display panel along an optical axis.Extraction features arranged on one or more surfaces of the waveguidewith a spatial distribution out-couple light received from the lightsource assembly towards the display panel. The display panel spatiallymodulates the out-coupled light from the waveguide according to data toform image light to be displayed to the user. For example, the displaypanel may be a liquid crystal display panel, some other display thatspatially modulates light to form image light, or some combinationthereof. The image light from the display panel is directed to theoptics block 730. The spatial distribution of extraction features mayoffset errors in brightness of the image light that reaches the eyeboxcaused by other components of the headset 705. The display block 725 maybe an embodiment of the display block 225 in FIGS. 2 and 3.

The optics block 730 magnifies image light received from the displayblock 725, corrects optical errors associated with the image light, andpresents the corrected image light to a user of the headset 705. Theoptics block 730 includes a plurality of optical elements (e.g., thatform a pancake lens assembly). Example optical elements included in theoptics block 730 include: an aperture, a Fresnel lens, a convex lens, aconcave lens, a filter, a reflecting surface, or any other suitableoptical element that affects image light. Moreover, the optics block 730may include combinations of different optical elements. In someembodiments, one or more of the optical elements in the optics block 730may have one or more coatings, such as partially reflective oranti-reflective coatings.

Magnification and focusing of the image light by the optics block 730allows the display block 725 to be physically smaller, weigh less andconsume less power than larger displays. Additionally, magnification mayincrease the field-of-view of the content presented by the display block725. For example, the field-of-view of the displayed content is suchthat the displayed content is presented using almost all (e.g.,approximately 110 degrees diagonal), and in some cases all, of theuser's field-of-view. Additionally in some embodiments, the amount ofmagnification may be adjusted by adding or removing optical elements.

In some embodiments, the optics block 730 may be designed to correct oneor more types of optical error. Examples of optical error include barrelor pincushion distortions, longitudinal chromatic aberrations, ortransverse chromatic aberrations. Other types of optical errors mayfurther include spherical aberrations, chromatic aberrations, errors dueto the lens field curvature, astigmatisms, any other type of opticalerror, or some combination thereof. In some embodiments, contentprovided to the display block 725 for display is pre-distorted, and theoptics block 730 corrects the distortion when it receives image lightfrom the display block 725 generated based on the content. The opticsblock 730 may be an embodiment of the optics block 230 in FIGS. 2 and 3.

The IMU 740 is an electronic device that generates data indicating aposition of the headset 705 based on measurement signals received fromone or more of the position sensors 735 and from depth informationreceived from the DCA 720. A position sensor 735 generates one or moremeasurement signals in response to motion of the headset 705. Examplesof position sensors 735 include: one or more accelerometers, one or moregyroscopes, one or more magnetometers, another suitable type of sensorthat detects motion, a type of sensor used for error correction of theIMU 740, or some combination thereof. The position sensors 735 may belocated external to the IMU 740, internal to the IMU 740, or somecombination thereof.

Based on the one or more measurement signals from one or more positionsensors 735, the IMU 740 generates data indicating an estimated currentposition of the headset 705 relative to an initial position of theheadset 705. For example, the position sensors 735 include multipleaccelerometers to measure translational motion (forward/back, up/down,left/right) and multiple gyroscopes to measure rotational motion (e.g.,pitch, yaw, roll). In some embodiments, the IMU 740 rapidly samples themeasurement signals and calculates the estimated current position of theheadset 705 from the sampled data. For example, the IMU 740 integratesthe measurement signals received from the accelerometers over time toestimate a velocity vector and integrates the velocity vector over timeto determine an estimated current position of a reference point on theheadset 705. Alternatively, the IMU 740 provides the sampled measurementsignals to the console 715, which interprets the data to reduce error.The reference point is a point that may be used to describe the positionof the headset 705. The reference point may generally be defined as apoint in space or a position related to the HMD's 705 orientation andposition.

The IMU 740 receives one or more parameters from the console 715. Theone or more parameters are used to maintain tracking of the headset 705.Based on a received parameter, the IMU 740 may adjust one or more IMUparameters (e.g., sample rate). In some embodiments, certain parameterscause the IMU 740 to update an initial position of the reference pointso it corresponds to a next position of the reference point. Updatingthe initial position of the reference point as the next calibratedposition of the reference point helps reduce accumulated errorassociated with the current position estimated the IMU 740. Theaccumulated error, also referred to as drift error, causes the estimatedposition of the reference point to “drift” away from the actual positionof the reference point over time. In some embodiments of the headset705, the IMU 740 may be a dedicated hardware component. In otherembodiments, the IMU 740 may be a software component implemented in oneor more processors.

The I/O interface 710 is a device that allows a user to send actionrequests and receive responses from the console 715. An action requestis a request to perform a particular action. For example, an actionrequest may be an instruction to start or end capture of image or videodata or an instruction to perform a particular action within anapplication. The I/O interface 710 may include one or more inputdevices. Example input devices include: a keyboard, a mouse, a gamecontroller, or any other suitable device for receiving action requestsand communicating the action requests to the console 715. An actionrequest received by the I/O interface 710 is communicated to the console715, which performs an action corresponding to the action request. Insome embodiments, the I/O interface 710 includes an IMU 740 thatcaptures calibration data indicating an estimated position of the I/Ointerface 710 relative to an initial position of the I/O interface 710.In some embodiments, the I/O interface 710 may provide haptic feedbackto the user in accordance with instructions received from the console715. For example, haptic feedback is provided when an action request isreceived, or the console 715 communicates instructions to the I/Ointerface 710 causing the I/O interface 710 to generate haptic feedbackwhen the console 715 performs an action.

The console 715 provides content to the headset 705 for processing inaccordance with information received from one or more of: the DCA 720,the headset 705, and the I/O interface 710. In the example shown in FIG.7, the console 715 includes an application store 755, a tracking module760, and an engine 765. Some embodiments of the console 715 havedifferent modules or components than those described in conjunction withFIG. 7. Similarly, the functions further described below may bedistributed among components of the console 715 in a different mannerthan described in conjunction with FIG. 7.

The application store 755 stores one or more applications for executionby the console 715. An application is a group of instructions, that whenexecuted by a processor, generates content for presentation to the user.Content generated by an application may be in response to inputsreceived from the user via movement of the headset 705 or the I/Ointerface 710. Examples of applications include: gaming applications,conferencing applications, video playback applications, or othersuitable applications.

The tracking module 760 calibrates the artificial reality system 700using one or more calibration parameters and may adjust one or morecalibration parameters to reduce error in determination of the positionof the headset 705 or of the I/O interface 710. For example, thetracking module 760 communicates a calibration parameter to the DCA 720to adjust the focus of the DCA 720 to more accurately determinepositions of structured light elements captured by the DCA 720.Calibration performed by the tracking module 760 also accounts forinformation received from the IMU 740 in the headset 705 and/or an IMU740 included in the I/O interface 710. Additionally, if tracking of theheadset 705 is lost (e.g., the DCA 720 loses line of sight of at least athreshold number of structured light elements), the tracking module 760may re-calibrate some or all of the artificial reality system 700.

The tracking module 760 tracks movements of the headset 705 or of theI/O interface 710 using information from the DCA 720, the one or moreposition sensors 735, the IMU 740 or some combination thereof. Forexample, the tracking module 760 determines a position of a referencepoint of the headset 705 in a mapping of a local area based oninformation from the headset 705. The tracking module 760 may alsodetermine positions of the reference point of the headset 705 or areference point of the I/O interface 710 using data indicating aposition of the headset 705 from the IMU 740 or using data indicating aposition of the I/O interface 710 from an IMU 740 included in the I/Ointerface 710, respectively. Additionally, in some embodiments, thetracking module 760 may use portions of data indicating a position orthe headset 705 from the IMU 740 as well as representations of the localarea from the DCA 720 to predict a future location of the headset 705.The tracking module 760 provides the estimated or predicted futureposition of the headset 705 or the I/O interface 710 to the engine 765.

The engine 765 generates a 3D mapping of the area surrounding some orall of the headset 705 (i.e., the “local area”) based on informationreceived from the headset 705. In some embodiments, the engine 765determines depth information for the 3D mapping of the local area basedon information received from the DCA 720 that is relevant for techniquesused in computing depth. The engine 765 may calculate depth informationusing one or more techniques in computing depth from one or morepolarized structured light patterns. In various embodiments, the engine765 uses the depth information to, e.g., update a model of the localarea, and generate content based in part on the updated model.

The engine 765 also executes applications within the artificial realitysystem 700 and receives position information, acceleration information,velocity information, predicted future positions, or some combinationthereof, of the headset 705 from the tracking module 760. Based on thereceived information, the engine 765 determines content to provide tothe headset 705 for presentation to the user. For example, if thereceived information indicates that the user has looked to the left, theengine 765 generates content for the headset 705 that mirrors the user'smovement in a virtual environment or in an environment augmenting thelocal area with additional content. Additionally, the engine 765performs an action within an application executing on the console 715 inresponse to an action request received from the I/O interface 710 andprovides feedback to the user that the action was performed. Theprovided feedback may be visual or audible feedback via the headset 705or haptic feedback via the I/O interface 710.

Additional Considerations

The foregoing description of the embodiments of the disclosure has beenpresented for the purpose of illustration; it is not intended to beexhaustive or to limit the disclosure to the precise forms disclosed.Persons skilled in the relevant art can appreciate that manymodifications and variations are possible in light of the abovedisclosure.

Some portions of this description describe the embodiments of thedisclosure in terms of algorithms and symbolic representations ofoperations on information. These algorithmic descriptions andrepresentations are commonly used by those skilled in the dataprocessing arts to convey the substance of their work effectively toothers skilled in the art. These operations, while describedfunctionally, computationally, or logically, are understood to beimplemented by computer programs or equivalent electrical circuits,microcode, or the like. Furthermore, it has also proven convenient attimes, to refer to these arrangements of operations as modules, withoutloss of generality. The described operations and their associatedmodules may be embodied in software, firmware, hardware, or anycombinations thereof.

Any of the steps, operations, or processes described herein may beperformed or implemented with one or more hardware or software modules,alone or in combination with other devices. In one embodiment, asoftware module is implemented with a computer program productcomprising a computer-readable medium containing computer program code,which can be executed by a computer processor for performing any or allof the steps, operations, or processes described.

Embodiments of the disclosure may also relate to an apparatus forperforming the operations herein. This apparatus may be speciallyconstructed for the required purposes, and/or it may comprise ageneral-purpose computing device selectively activated or reconfiguredby a computer program stored in the computer. Such a computer programmay be stored in a non-transitory, tangible computer readable storagemedium, or any type of media suitable for storing electronicinstructions, which may be coupled to a computer system bus.Furthermore, any computing systems referred to in the specification mayinclude a single processor or may be architectures employing multipleprocessor designs for increased computing capability.

Embodiments of the disclosure may also relate to a product that isproduced by a computing process described herein. Such a product maycomprise information resulting from a computing process, where theinformation is stored on a non-transitory, tangible computer readablestorage medium and may include any embodiment of a computer programproduct or other data combination described herein.

Finally, the language used in the specification has been principallyselected for readability and instructional purposes, and it may not havebeen selected to delineate or circumscribe the inventive subject matter.It is therefore intended that the scope of the disclosure be limited notby this detailed description, but rather by any claims that issue on anapplication based hereon. Accordingly, the disclosure of the embodimentsis intended to be illustrative, but not limiting, of the scope of thedisclosure, which is set forth in the following claims.

What is claimed is:
 1. A headset comprising: a display block including:a waveguide configured to receive light from a light source assembly, aplurality of extraction features that have a spatial distribution acrossone or more surfaces of the waveguide, wherein the plurality ofextraction features out-couple light from the waveguide, and the spatialdistribution is such that out-coupled light has a first non-uniformbrightness distribution, and a display panel configured to modulate theout-coupled light to form image light, wherein the image light has abrightness distribution based in part on the first non-uniformbrightness distribution; and an optics block including one or moreoptical elements configured to direct the image light to an eyebox, andthe optics block adds a second non-uniform brightness distribution thatis offset by the first non-uniform brightness distribution, such thatthe image light directed to the eyebox has a target brightnessdistribution.
 2. The headset of claim 1, wherein the brightnessdistribution of the image light output from the display panel includesan error brightness distribution, and the first non-uniform brightnessdistribution offsets the error brightness distribution.
 3. The headsetof claim 1, wherein the extraction features are selected from a groupconsisting of: half-dome structures, prism structures protruding, dots,some other structures that cause light to out-couple from the waveguide,and some combination thereof.
 4. The headset of claim 1, wherein the oneor more surfaces of the waveguide include a first surface and a secondsurface that is opposite to the first surface, the first surface iscloser to the eyebox than the second surface, and the spatialdistribution of the plurality of extraction features is across the firstsurface.
 5. The headset of claim 1, wherein the one or more surfaces ofthe waveguide include a first surface and a second surface that isopposite to the first surface, the first surface is closer to the eyeboxthan the second surface, and the spatial distribution of the pluralityof extraction features is across the second surface.
 6. The headset ofclaim 1, wherein the one or more surfaces of the waveguide include afirst surface and a second surface that is opposite to the firstsurface, the first surface is closer to the eyebox than the secondsurface, and the spatial distribution of the plurality of extractionfeatures is across the second surface and the first surface.
 7. Theheadset of claim 1, wherein the spatial distribution of extractionfeatures has a center region and a peripheral region that circumscribesthe center region, and wherein a spatial density of the extractionfeatures is higher in the peripheral region than in the center region.8. The headset of claim 7, wherein the spatial density of the extractionfeatures in the peripheral region increases as a function of distancefrom an on-axis intersection point of the waveguide and an optical axisof the display block.
 9. The headset of claim 1, wherein the spatialdistribution of extraction features is such that a spatial density ofextraction features increases as a function of distance from an on-axisintersection point of the waveguide and an optical axis of the displayblock.
 10. The headset of claim 1, wherein the target brightnessdistribution is a uniform distribution.
 11. The headset of claim 1,wherein the one or more optical elements includes a first opticalelement and a second optical element that form a pancake lens assembly.12. The headset of claim 1, wherein the headset is a head-mounteddisplay.
 13. A display block comprising: a light source assembly; awaveguide configured to receive light from the light source assembly; aplurality of extraction features that have a spatial distribution acrossone or more surfaces of the waveguide, wherein the plurality ofextraction features out-couple light from the waveguide, and the spatialdistribution is such that out-coupled light has a first non-uniformbrightness distribution; and a display panel configured to modulate theout-coupled light to form image light, wherein the image light has abrightness distribution based in part on the first non-uniformbrightness distribution, wherein an optics block including a firstoptical element and a second optical element that together generate afolded optical system that is configured to direct the image light to aneyebox, and the folded optical system adds a second non-uniformbrightness distribution that is offset by the first non-uniformbrightness distribution, such that the image light directed to theeyebox has a target brightness distribution.
 14. The display block ofclaim 13, wherein the brightness distribution of the image light outputfrom the display panel includes an error brightness distribution, andthe first non-uniform brightness distribution offsets the errorbrightness distribution.
 15. The display block of claim 13, wherein theone or more surfaces of the waveguide include a first surface and asecond surface that is opposite to the first surface, the first surfaceis closer to the eyebox than the second surface, and the spatialdistribution of the plurality of extraction features is across the firstsurface.
 16. The display block of claim 13, wherein the one or moresurfaces of the waveguide include a first surface and a second surfacethat is opposite to the first surface, the first surface is closer tothe eyebox than the second surface, and the spatial distribution of theplurality of extraction features is across the second surface.
 17. Thedisplay block of claim 13, wherein the one or more surfaces of thewaveguide include a first surface and a second surface that is oppositeto the first surface, the first surface is closer to the eyebox than thesecond surface, and the spatial distribution of the plurality ofextraction features is across the second surface and the first surface.18. The display block of claim 13, wherein the spatial distribution ofextraction features has a center region and a peripheral region thatcircumscribes the center region, and wherein a spatial density of theextraction features is higher in the peripheral region than in thecenter region.
 19. The display block of claim 13, wherein the spatialdistribution of extraction features is such that a spatial density ofextraction features increases as a function of distance from an on-axisintersection point of the waveguide and an optical axis of the displayblock.
 20. The display block of claim 13, wherein the target brightnessdistribution is a uniform distribution.